There are a variety of composite products currently available. These include, but should not be limited to, Fibreboard (MDF etc), Oriented Strand Board (OSB), Waferboard, amongst others. For the purposes of this specification such products, as they contain lignocellulosic material, will be referred to as lignocellulosic composite products for ease of reference.
There are many advantages in using lignocellulosic composite products in the place of raw timber. These include the ability to prepare a finished-looking timber product for immediate use, as well as the ability to use what would otherwise be waste material, in an effective and productive manner. In addition, the more use that can be made of waste timber products, the less natural timber will be needed. Typically, untreated soft wood timber composite products, and building materials formed from composite products made from reconstituted products material, have been found not to be sufficiently strong to fulfil the same functions as a hard wood timber. Furthermore, such products if untreated have a tendency to absorb moisture thereby causing the material to expand and suffer deterioration.
Usually, the manufacture of lignocellulosic composite products uses lignocellulosic particles (eg sawdust, bark, husks and the like) which are mixed with a binder composition. The binders can be broadly grouped into formaldehyde-based binders, polyurethane-type binders, phenolic-based and isocyanate-based binder products. In many cases, especially “phenolic line” production, toxic by-products are produced and the secure disposal of strips, off-cuts and contaminated water can be costly. Furthermore, considerable energy needs to be expended as the material has to be dried to approximately five percent (5%) moisture in order to cure the phenolic plastic. Such techniques have been used to improve the strength and water resistance of such materials.
It is also known to use plastics material in the manufacture of lignocellulosic composite board products. Usually, the amount of plastics materials in the starting material, (i.e. with the lignocellulosic particles) is around 50% by weight of the starting mixture. The plastic material is melted and the molten plastic and lignocellulosic material are blended and are then extruded through a die. Such a process does not require the presence of an additional binder (eg a phenolic-based binder or the like) but does require the use of a coupling agent to allow the lignocellulosic material to bind to the plastics material. The use of approximately 50% of plastics material in the manufacture of such composite board product, results in a product having a plastic appearance which is not always acceptable to consumers.
Lowering the amount of plastics material used in the manufacture of extruded composite board products, eg down to about 20% plastics material by weight, is also possible, provided the lignocellulosic particles used in the product are finer than about 40 mesh. Such processes still require the use of coupling agents but allow less plastic to be used and lessen the plastic look of the product. There is an inherent limitation in the process as a result of particle size restriction.
There would be distinct advantages in being able to make a composite board using a binder that includes a plastics material at even lower levels, if a product of adequate material characteristics can be produced using a broad range of particle sizes while minimising the plastic look being imparted to the final product. In addition, the less plastics material used, the lower the cost of production will be in general terms.
The ability to manufacture composite board products using substrates other than lignocellulosic material (eg rubber, non-recyclable plastics materials etc) would also be advantageous in terms of waste material use.
For the purposes of this specification the phrase “composite product” (without further qualification—eg lignocellulosic) should be taken to include reference to the use of lignocellulosic material, rubber or non-recyclable plastics material as the substrate from which the composite board product is made.